Pressure Reducing Valves & Expansion Tanks
Pressure Reducing Valves (PRVs) and Expansion Tanks
Pressure Reducing Valves (PRVs)
These valves are not required but are recommended in most areas of our gravity fed distribution system. Installed directly after the water meter in homes,
commercial buildings, and manufacturing plants, a water pressure reducing valve automatically reduces the pressure from the water supply main to a lower, more sensible pressure.
There are two types of water pressure reducing valves-- direct acting and pilot operated. Direct acting valves are the more popular water pressure reducing valves, consisting of globe-type bodies with a spring-loaded, heat-resistant diaphragm connected to the outlet of the valve that acts upon a spring. This spring holds a pre-set tension on the valve seat installed with a pressure equalizing mechanism for precise water pressure control. These are the types that are found in our customer’s homes.
Expansion tanks are not required in our system but are recommended. Potable water expansion tanks are designed to absorb the increased volume of water created by thermal expansion and maintain a balanced pressure throughout the potable water supply system. They are used to prevent plumbing system and/or water heater damage as well as unnecessary relief valve discharge caused by excessive pressure from thermal expansion.
How It Works
When water is heated, its density decreases, and volume expands. Because water is not compressible, the extra volume created by expansion needs somewhere to go. During no-flow periods in a system, pressure reducing valves, backflow preventers, and other one-way valves are closed, thus eliminating a path for expanded water to flow back to the system supply. That is when system pressure increases, causing a number of undesirable and potentially dangerous problems.
When the water volume increases with nowhere to go, an expansion tank allows excess water to enter the pre-pressurized tank. As the temperature and pressure reaches its maximum, the diaphragm flexes against an air cushion to allow for increased water expansion, because unlike water, air is compressible. When the system is opened again or the water cools, water leaves the tank and returns to the system.